Fuel injector diagnostic for dual fuel engine

ABSTRACT

Various systems and methods are described for controlling fuel injection of a dual fuel engine which includes first and second fuel rails and first and second fuel pumps. In one example, while pumping is suspended in the second fuel rail, the first fuel is injected to all but one cylinder of the engine and the second fuel is injected to the one cylinder in a predetermined sequence. As such, the fuel injector injecting to the one cylinder is isolated and its performance may be assessed without significantly affecting engine performance.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/756,838 filed Apr. 8, 2010, the entire contents of which areincorporated herein by reference for all purposes.

TECHNICAL FIELD

The present application relates to diagnosing injector variability in afuel injection system in a dual fuel engine.

BACKGROUND AND SUMMARY

When new, fuel injectors may exhibit some piece-to-piece variability.Over time, injector performance may degrade (e.g., injector becomesclogged) which may further increase piece-to-piece injector variability.As a result, the actual amount of fuel injected to each cylinder of anengine may not be the desired amount and the difference between theactual and desired amounts may vary between injectors. Suchdiscrepancies can lead to reduced fuel economy, increased tailpipeemissions, and an overall decrease in engine efficiency. Further,engines operating with a plurality of different injection substances,such as different fuel mixtures, may have even more fuel injectors(e.g., twice as many) resulting in a greater possibility for degradationof engine performance due to injector degradation.

The inventor herein has recognized the above problems and has devised anapproach to at least partially address them. Thus, a method forcontrolling fuel injection of a dual multi-substance injection enginewhich includes first and second fuel rails and first and second fuelpumps is disclosed. The method comprises, suspending pumping of a secondsubstance into the second fuel rail and injecting a first substance toall but a single cylinder of the engine, and, while pumping is suspendedin the second fuel rail, injecting the second substance into the singlecylinder and correlating pressure decrease in the second fuel rail toinjector operation.

By suspending pumping in the second fuel rail, an injector can beisolated and pressure drops in the fuel rail can be correlated to theoperation of the injector. Further, injection of the first fuel cancontinue without interruption in all but one of the cylinders. In thismanner, each fuel injector can be isolated and tested withoutsignificantly affecting engine operation.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine.

FIG. 2 shows a schematic diagram of a dual fuel system.

FIG. 3 shows a flow chart illustrating a routine for

FIG. 4 shows a flow chart illustrating an example fuel injectordiagnostic routine.

FIG. 5 shows a flow chart illustrating an example fuel pump diagnosticroutine.

FIGS. 6A and 6B show an example fuel injection timing and fuel pressurechange during a diagnostic routine.

FIGS. 7A and 7B show another example of fuel injection timing and fuelpressure change during a diagnostic routine.

DETAILED DESCRIPTION

The following description relates to a method for controlling fuelinjection in a multi-injection substance engine, such as a dual fuelengine, which includes first and second fuel rails and first and secondfuel pumps. In one example, a diagnostic routine may be carried out inthe following manner: pumping of a second fuel into the second fuel railis suspended while a first fuel is injected to all but a single cylinderof the engine. Further, while pumping is suspended in the second fuelrail, the second fuel is injected into the single cylinder and thepressure decrease in the second fuel rail is correlated to injectoroperation. In this manner, a single injector may be isolated at one timeallowing the injector to be tested without having a substantial impacton the performance of the engine. Furthermore, all injectors for bothtypes of fuel can be tested in this manner. In another example, asub-group of cylinders may be isolated together, rather than a singlecylinder as noted above.

FIG. 1 shows one cylinder of a multi-cylinder engine, as well as theintake and exhaust path connected to that cylinder. In the embodimentshown in FIG. 1, engine 10 is capable of using two different substances,and/or two different injectors in one example. For example, engine 10may use gasoline and an alcohol containing fuel such as ethanol,methanol, a mixture of gasoline and ethanol (e.g., E85 which isapproximately 85% ethanol and 15% gasoline), a mixture of gasoline andmethanol (e.g., M85 which is approximately 85% methanol and 15% gas),etc. Further, as another example, engine 10 may use one fuel or fuelblend (e.g., gasoline or gasoline and ethanol) and one mixture of waterand fuel (e.g., water and methanol). As another example, engine 10 mayuse gasoline and a reformate fuel generated in a reformer coupled to theengine. In another example, two fuel systems are used, but each uses thesame fuel, such as gasoline. In still another embodiment, a singleinjector (such as a direct injector) may be used to inject a mixture ofgasoline and an alcohol based fuel, where the ratio of the two fuelquantities in the mixture may be adjusted by controller 12 via a mixingvalve, for example. In still another example, two different injectorsfor each cylinder are used, such as port and direct injectors. In evenanother embodiment, different sized injectors, in addition to differentlocations and different fuels, may be used.

FIG. 1 shows one example fuel system with two fuel injectors percylinder, for at least one cylinder. Further, each cylinder may have twofuel injectors. The two injectors may be configured in variouslocations, such as two port injectors, one port injector and one directinjector (as shown in FIG. 1), or others.

Continuing with FIG. 1, it shows a dual injection system, where engine10 has both direct and port fuel injection, as well as spark ignition.Internal combustion engine 10, comprising a plurality of combustionchambers, is controlled by electronic engine controller 12. Combustionchamber 30 of engine 10 is shown including combustion chamber walls 32with piston 36 positioned therein and connected to crankshaft 40. Astarter motor (not shown) may be coupled to crankshaft 40 via a flywheel(not shown), or alternatively direct engine starting may be used.

In one particular example, piston 36 may include a recess or bowl (notshown) to help in forming stratified charges of air and fuel, ifdesired. However, in an alternative embodiment, a flat piston may beused.

Combustion chamber, or cylinder, 30 is shown communicating with intakemanifold 44 and exhaust manifold 48 via respective intake valves 52 aand 52 b (not shown), and exhaust valves 54 a and 54 b (not shown).Thus, while four valves per cylinder may be used, in another example, asingle intake and single exhaust valve per cylinder may also be used. Instill another example, two intake valves and one exhaust valve percylinder may be used.

Combustion chamber 30 can have a compression ratio, which is the ratioof volumes when piston 36 is at bottom center to top center. In oneexample, the compression ratio may be approximately 9:1. However, insome examples where different fuels are used, the compression ratio maybe increased. For example, it may be between 10:1 and 11:1 or 11:1 and12:1, or greater.

Fuel injector 66A is shown directly coupled to combustion chamber 30 fordelivering injected fuel directly therein in proportion to the pulsewidth of signal dfpw received from controller 12 via electronic driver68. While FIG. 1 shows injector 66A as a side injector, it may also belocated overhead of the piston, such as near the position of spark plug92. Such a position may improve mixing and combustion due to the lowervolatility of some alcohol based fuels. Alternatively, the injector maybe located overhead and near the intake valve to improve mixing.

Fuel may be delivered to fuel injector 66A by a high pressure fuelsystem (shown in FIG. 2) including a fuel tank, fuel pumps, and a fuelrail. Alternatively, fuel may be delivered by a single stage fuel pumpat lower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tank(or tanks) may (each) have a pressure transducer providing a signal tocontroller 12.

Fuel injector 66B is shown coupled to intake manifold 44, rather thandirectly to cylinder 30. Fuel injector 66B delivers injected fuel inproportion to the pulse width of signal pfpw received from controller 12via electronic driver 68. Note that a single driver 68 may be used forboth fuel injection systems, or multiple drivers may be used. Fuelsystem 164 is also shown in schematic form delivering vapors to intakemanifold 44.

Further, engine 10 may include fuel reformer 97 with storage tank 93 forsupplying a gaseous fuel to one or both fuel injectors 66 a and 66 b.Gaseous fuel may be supplied to one or both fuel injectors from storagetank 93 by way of pump 96 and check valve 82. Pump 96 pressurizesgaseous fuel supplied from fuel reformer 97 in storage tank 93. Checkvalve 82 limits flow of gaseous fuel from storage tank 93 to fuelreformer 97 when the output of pump 96 is at a lower pressure thanstorage tank 93. In some embodiments, check valve 82 may be positionedupstream of pump 96. In other embodiments, check valve 82 may bepositioned in parallel with pump 96. Further, check valve 82 may insteadbe an actively controlled valve. In such an embodiment, the activelycontrolled valve would be opened when the pump is operating. The controlsignal to pump 96 may be a simple on/off signal, for example. In otherexamples, the control signal may be a continuous variable voltage,current, pulse width, desired speed, or desired flowrate, etc. Further,pump 96 may be turned off, slowed down, or disabled with one or morebypass valves (not shown).

Fuel reformer 97 includes catalyst 72 and may further include optionalelectrical heater 98 for reforming alcohol supplied from fuel tank 91.Fuel reformer 97 is shown coupled to the exhaust system downstream ofcatalyst 70 and exhaust manifold 48. However, fuel reformer 97 may becoupled to exhaust manifold 48 and located upstream of catalyst 70. Fuelreformer 97 may use exhaust heat to drive an endothermic dehydrogenationof alcohol supplied by fuel tank 91 and to promote fuel reformation.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of elliptical throttleplate 62 is controlled by controller 12 via electric motor 94. Thisconfiguration may be referred to as electronic throttle control (ETC),which can also be utilized during idle speed control. In an alternativeembodiment (not shown), a bypass air passageway is arranged in parallelwith throttle plate 62 to control inducted airflow during idle speedcontrol via an idle control by-pass valve positioned within the airpassageway.

Exhaust gas sensor 76 is shown coupled to exhaust manifold 48 upstreamof catalytic converter 70 (where sensor 76 can correspond to variousdifferent sensors). For example, sensor 76 may be any of many knownsensors for providing an indication of exhaust gas air/fuel ratio suchas a linear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, aHEGO, or an HC or CO sensor. In this particular example, sensor 76 is atwo-state oxygen sensor that provides signal EGO to controller 12 whichconverts signal EGO into two-state signal EGOS. A high voltage state ofsignal EGOS indicates exhaust gases are rich of stoichiometry and a lowvoltage state of signal EGOS indicates exhaust gases are lean ofstoichiometry. Signal EGOS may be used to advantage during feedbackair/fuel control to maintain average air/fuel at stoichiometry during astoichiometric homogeneous mode of operation. Further details ofair-fuel ratio control are included herein.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to spark advance signal SA fromcontroller 12.

Controller 12 may cause combustion chamber 30 to operate in a variety ofcombustion modes, including a homogeneous air/fuel mode and a stratifiedair/fuel mode by controlling injection timing, injection amounts, spraypatterns, etc. Further, combined stratified and homogenous mixtures maybe formed in the chamber. In one example, stratified layers may beformed by operating injector 66A during a compression stroke. In anotherexample, a homogenous mixture may be formed by operating one or both ofinjectors 66A and 66B during an intake stroke (which may be open valveinjection). In yet another example, a homogenous mixture may be formedby operating one or both of injectors 66A and 66B before an intakestroke (which may be closed valve injection). In still other examples,multiple injections from one or both of injectors 66A and 66B may beused during one or more strokes (e.g., intake, compression, exhaust,etc.). Even further examples may be where different injection timingsand mixture formations are used under different conditions, as describedbelow.

Controller 12 can control the amount of fuel delivered by fuel injectors66A and 66B so that the homogeneous, stratified, or combinedhomogenous/stratified air/fuel mixture in chamber 30 can be selected tobe at stoichiometry, a value rich of stoichiometry, or a value lean ofstoichiometry.

Controller 12 is shown as a microcomputer, including microprocessor unit102, input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 106 inthis particular example, random access memory 108, keep alive memory110, and a conventional data bus. Controller 12 is shown receivingvarious signals from sensors coupled to engine 10, in addition to thosesignals previously discussed, including measurement of inducted mass airflow (MAF) from mass air flow sensor 100 coupled to throttle body 58;engine coolant temperature (ECT) from temperature sensor 112 coupled tocooling sleeve 114; a profile ignition pickup signal (PIP) from Halleffect sensor 118 coupled to crankshaft 40; and throttle position TPfrom throttle position sensor 120; absolute Manifold Pressure Signal MAPfrom sensor 122; an indication of knock from knock sensor 182; and anindication of absolute or relative ambient humidity from sensor 180.Engine speed signal RPM is generated by controller 12 from signal PIP ina conventional manner and manifold pressure signal MAP from a manifoldpressure sensor provides an indication of vacuum, or pressure, in theintake manifold. During stoichiometric operation, this sensor can givean indication of engine load. Further, this sensor, along with enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In a one example, sensor 118, which is also used as anengine speed sensor, produces a predetermined number of equally spacedpulses every revolution of the crankshaft.

Continuing with FIG. 1, a variable camshaft timing system is shown.Specifically, camshaft 130 of engine 10 is shown communicating withrocker arms 132 and 134 for actuating intake valves 52 a, 52 b andexhaust valves 54 a, 54 b. Camshaft 130 is directly coupled to housing136. Housing 136 forms a toothed wheel having a plurality of teeth 138.Housing 136 is hydraulically coupled to crankshaft 40 via a timing chainor belt (not shown). Therefore, housing 136 and camshaft 130 rotate at aspeed substantially equivalent to the crankshaft. However, bymanipulation of the hydraulic coupling as will be described laterherein, the relative position of camshaft 130 to crankshaft 40 can bevaried by hydraulic pressures in advance chamber 142 and retard chamber144. By allowing high pressure hydraulic fluid to enter advance chamber142, the relative relationship between camshaft 130 and crankshaft 40 isadvanced. Thus, intake valves 52 a, 52 b and exhaust valves 54 a, 54 bopen and close at a time earlier than normal relative to crankshaft 40.Similarly, by allowing high pressure hydraulic fluid to enter retardchamber 144, the relative relationship between camshaft 130 andcrankshaft 40 is retarded. Thus, intake valves 52 a, 52 b, and exhaustvalves 54 a, 54 b open and close at a time later than normal relative tocrankshaft 40.

Continuing with the variable cam timing system, teeth 138, being coupledto housing 136 and camshaft 130, allow for measurement of relative camposition via cam timing sensor 150 providing signal VCT to controller12. Teeth 1, 2, 3, and 4 are preferably used for measurement of camtiming and are equally spaced (for example, in a V-8 dual bank engine,spaced 90 degrees apart from one another) while tooth 5 is preferablyused for cylinder identification. In addition, controller 12 sendscontrol signals (LACT, RACT) to conventional solenoid valves (not shown)to control the flow of hydraulic fluid either into advance chamber 142,retard chamber 144, or neither.

Relative cam timing can be measured in a variety of ways. In generalterms, the time, or rotation angle, between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

Sensor 160 may also provide an indication of oxygen concentration in theexhaust gas via signal 162, which provides controller 12 a voltageindicative of the O2 concentration. For example, sensor 160 can be aHEGO, UEGO, EGO, or other type of exhaust gas sensor. Also note that, asdescribed above with regard to sensor 76, sensor 160 can correspond tovarious different sensors.

As described above, FIG. 1 merely shows one cylinder of a multi-cylinderengine, and that each cylinder has its own set of intake/exhaust valves,fuel injectors, spark plugs, etc.

Also, in the example embodiments described herein, the engine may becoupled to a starter motor (not shown) for starting the engine. Thestarter motor may be powered when the driver turns a key in the ignitionswitch on the steering column, for example. The starter is disengagedafter engine starting, for example, by engine 10 reaching apredetermined speed after a predetermined time. Further, in thedisclosed embodiments, an exhaust gas recirculation (EGR) system may beused to route a desired portion of exhaust gas from exhaust manifold 48to intake manifold 44 via an EGR valve (not shown). Alternatively, aportion of combustion gases may be retained in the combustion chambersby controlling exhaust valve timing.

FIG. 2 illustrates a fuel injection system 200 with a high pressure dualfuel rail system which may be the fuel system coupled to engine 10 inFIG. 1, for example. The system 200 may include fuel tanks 201 a and 201b, low pressure (or lift) fuel pumps 202 a and 202 b that supply fuelfrom the fuel tanks 201 a and 201 b to high pressure fuel pumps 206 aand 206 b via low pressure passages 204 a and 204 b, respectively. Thehigh pressure fuel pumps 206 a and 206 b supply pressurized fuel to thehigh pressure fuel rails 210 a and 210 b via high pressure passages 208a and 208 b, respectively. The high pressure fuel rail 210 a suppliespressurized fuel to fuel injectors 214 a, 214 b, 214 c, and 214 d andthe high pressure fuel rail 210 b supplies pressurized fuel to fuelinjectors 214 e, 214 f, 214 g, and 214 h. The fuel injectors injectfuels into engine cylinders 212 a, 212 b, 212 c, and 212 d located in anengine block 216. Un-injected fuel may be returned to the fuel tanks 201a and 201 b via respective fuel return passages (not shown). The engineblock 216 may be coupled to an intake pathway 222 with an intake airthrottle 224.

The system may further include a control unit 226. Similar to controlunit 12 in FIG. 1, the control unit may be further coupled to variousother sensors 252 and various actuators 254 (e.g., fuel injectionactuator, spark ignition actuator, throttle valve actuator, etc) forsensing and controlling vehicle operating conditions. For example, thecontrol unit 226 may sense engine speed, throttle position, intaketemperature and/or pressure, exhaust temperature/pressure, mass airflow, engine coolant temperature, crank angle position, variable camposition, injection timing, spark ignition timing through appropriatesensors. The control unit 226 may also control operations of intakeand/or exhaust valves or throttles, engine cooling fan, spark ignition,injector, and fuel pumps to control engine operating conditions.

FIG. 2 shows additional details of the fuel injection system.Specifically, FIG. 2 shows control unit 226, which may be an enginecontrol unit, powertrain control unit, control system, a separate unit,or combinations of various control units. The control unit 226 is shownin FIG. 2 as a microcomputer, including an input/output (I/O) port 228,a central processing unit (CPU) 232, an electronic storage medium forexecutable programs and calibration values shown as read only memory(ROM) chip 230 in this particular example, random access memory (RAM)234, keep alive memory (KAM) 136, and a data bus.

The control unit 226 may receive signals from various sensors. Forexample, the control unit 226 may receive fuel pressure signals from thehigh pressure fuel rails 210 a and 210 b via respective fuel pressuresensors 220 a and 220 b located in the high pressure fuel rails 210 aand 210 b. The control unit may further receive throttle opening anglesignals (O_(A)) indicating the intake air throttle position via athrottle position sensor 238, intake air flow signals (Q_(a)) from amass air flow sensor 240, engine speed signals (N_(e)) from engine speedsensor 242, accelerator pedal position signal from a pedal 244 via anaccelerator pedal position sensor 246, crank angle sensor 248, andengine coolant temperature (ECT) signals from engine temperature sensor250.

In addition to the signals mentioned above, the control unit 226 mayalso receive other signals from various other sensors 252. For example,the control unit 226 may receive a profile ignition pickup signal (PIP)from a Hall effect sensor (not shown) coupled to a crankshaft and amanifold pressure signal MAP from a manifold pressure sensor, as shownin FIG. 1.

The control unit 226 may control operations of various vehicularcomponents via various actuators 254. For example, the control unit 226may control the operation of the fuel injectors 214 a-h throughrespective fuel injector actuators (not shown) and high pressure fuelpumps 206 a and 206 b through respective high pressure fuel pumpactuators (not shown).

The high pressure fuel pumps 206 a and 206 b may be coupled to andcontrolled by the control unit 226 as is shown in FIG. 2. The controlunit 226 may regulate the amount or speed of fuel to be fed into thehigh pressure rails 210 a and 210 b by the high pressure fuel pumps 206a and 206 b through respective high pressure fuel pump controls (notshown). The control unit 226 may also completely stop fuel supply to thehigh pressure fuel rails 210 a and 210 b. Furthermore, the high pressurefuel pumps 206 a and 206 b may contain one or more relief valves thatdecrease the fuel pressure in the high pressure fuel rails when the fuelpressure in the high pressure fuel rails 210 a and 210 b is higher thandesired.

Although the injectors are coupled to engine cylinders in this example,in other examples, the injectors may be coupled to an intake pathway.The fuel injectors that are directly coupled to engine cylinders may belocated overhead of cylinder pistons (not shown) or located on the sideof an engine cylinder. The injectors 214 a-h may be operatively coupledto and controlled by a control unit, such as the control unit 226, as isshown in FIG. 2. An amount of fuel injected from the injector and theinjection timing may be determined by the control unit 226 from anengine map stored in the control unit 226 on the basis of engine speed(N_(e)) and/or intake throttle angle (Q_(A)), or engine load. Theinjector may be controlled via controlling an electromagnetic valvecoupled to the injector (not shown). The injector may not inject all thefuel supplied to the injector and may return part of the fuel suppliedto the fuel tank through a return path, such as a return passage (notshown).

The high pressure fuel rails 210 a and 210 b may also contain one ormore temperature sensors for sensing the fuel temperature in the highpressure fuel rails 210 a and 210 b and one or more pressure sensors forsensing the fuel pressure in the high pressure fuel rails 210 a and 210b. They may also contain one or more relief valves that when openeddecrease the pressure in the high pressure fuel rails when it is greaterthan desired and return extra fuel back to the fuel tank via a fuelreturn passage.

Various other modifications or adjustments may be made to the aboveexample systems. For example, the fuel passages (e.g., 204 a, 204 b, 208a, and 208 b) may contain one or more filters, pumps, pressure sensors,temperature sensors, and/or relief valves. The fuel passages may includeone or multiple lines. There may be one or more fuel cooling systems.The intake pathway 222 may contain one or more air filters,turbochargers, and/or surge tanks. The engine may contain one or moreengine cooling fans, cooling circuits, spark ignitions, valves, andcontrols. The engine may be coupled to an exhaust pathway.

Continuing to FIG. 3, a routine 300 for determining if a diagnosticroutine should be run is illustrated. Specifically, routine 300determines if a diagnostic routine is desired based on which fuels aredesired for engine operation and an amount of time since the lastinjector calibration. For example, during conditions in which both fuelsare needed, a diagnostic routine may not be run since injection of oneof the fuels is suspended one of the cylinders.

At 310 of routine 300, engine operating conditions are determined.Engine operating conditions may include load, temperature, speed, etc.

Once the engine operation conditions are determined, routine 300proceeds to 312 where it is determined if both fuels are desired forengine operation. For example, if the engine is operating at high load,injection of both fuels may be desired in order to continue operating athigh load. As another example, the engine may be operating under lowload conditions and the engine may operate using one or both fuels.

If it is determined that both fuels are desired, routine 300 moves to318 and the current engine operation is continued and the routine ends.On the other hand, if it is determined that both fuels are not desiredfor operation (e.g., one or both fuels may be used, but both fuels arenot needed for optimum engine efficiency), routine 300 continues to 314where it is determined if the time since the last injector calibrationis greater than or equal to a predetermined threshold. As examples,injector calibration may be desired one or more times per drive cycle,every other drive cycle, or after a predetermined number of miles isdriven.

If the time since the last injector calibration is not greater than orequal to the predetermined threshold, routine 300 ends. In contrast, ifthe time since the last injector calibration is greater than or equal tothe predetermined threshold, routine 300 proceeds to 316 and an injectordiagnostic routine is carried out, as will be described below withreference to FIG. 4.

Continuing to FIG. 4, a diagnostic routine 400 for fuel injectors isillustrated. Specifically, routine 400 suspends the pumping of fuel intoone of the fuel rails and fuel is injected to a single cylinder or agroup of cylinders at a time in order to detect a pressure drop due tothe injection. As such, the other fuel rail pump may continue to supplyfuel to the other fuel rail and other cylinders of the engine and thediagnostic routine may be carried out using one injector at a timethereby maintaining engine efficiency.

At 410 of routine 400, pumping of fuel B is suspended in fuel rail B.For example, in a dual fuel system, the fuel system may include a firstfuel rail (e.g., fuel rail A) coupled to a first fuel pump (e.g., fuelpump A) which pumps a first fuel (e.g., fuel A) into the first fuel railand a second fuel rail (e.g., fuel rail B) coupled to a second fuel pump(e.g., fuel pump B) which pumps a second fuel (e.g., fuel B) into thesecond fuel rail. Fuel A and fuel B may be various fuels such asgasoline, ethanol, a gaseous reformate fuel, a blend of gasoline and analcohol based fuel, a mixture of fuel and water, etc.

After the pumping of fuel B is suspended in fuel rail B, injection offuel A is carried out in all but one of the cylinders of the engine at412 of routine 400. For example, if pumping of fuel B is suspended infuel rail B, fuel A is injected to all but a single cylinder. As anexample, in a four cylinder engine, fuel A may be injected to cylinders2, 3, and 4, but not cylinder 1. In some embodiments, injection of fuelA may be suspended in a group of cylinders instead of a single cylinder,for example, fuel A may be injected to cylinders 1, 2, and 3 and notcylinders 4, 5, and 6 in a six cylinder engine example.

Next, while the pumping of fuel B is suspended in fuel rail B and theinjection of fuel A is carried out in all but a single cylinder of theengine, fuel B is injected to the single cylinder at 414 of routine 400.In some examples, fuel B may be injected to the single cylinder in apredetermined sequence for a predetermined number of times. For example,FIG. 6A shows an example in which only one injector is fired in asequence. In other examples, fuel B may be injected to more than onecylinder (but only one cylinder at a time) in a predetermined sequence.As an example, FIG. 7A shows an example in which four differentinjectors are fired at different times in a sequence.

Because pumping has been suspended in fuel rail B, the amount of fuel,and thus the pressure, decreases with each injection, thus the pressuredrop due to the injection of fuel in the single cylinder can becorrelated to injector degradation at 416 of routine 400 and injectordegradation is indicated at 418 of routine 400. For example, if thechange in pressure (e.g., pressure drop) is lower than expected, theinjector may be partially plugged and less fuel is injected thandesired. In another example, if the pressure drop is lower than expectedat small pulse widths (e.g., a short amount of time between eachinjection in the sequence), the injector may be slow to open and lessfuel is injected than desired. In yet another example, if the pressuredrop is higher than expected, the injector may be stuck open and morefuel is injected than desired. As another example, if the pressure dropis higher than expected at small pulse widths, the injector may be slowto close and more fuel is injected than desired.

At 420, it is determined if a pump diagnostic routine is desired. Aswith the injector diagnostic routine, it may be desired to run a pumpdiagnostic routine at predetermined intervals, for example, one or moretimes per drive cycle or after a predetermined number of miles aredriven. If it is determined that a pump diagnostic routine is desired,routine 400 moves to 426 and routine 500 (e.g., a pump diagnosticroutine) of FIG. 5 commences.

On the other hand, if it is determined that a pump diagnostic routine isnot desired, routine 400 proceeds to 422 and pumping of fuel B into fuelrail B is resumed. Next, at 424, the amount of fuel injected to thesingle cylinder by the injector is adjusted based on the correlation.For example, if the amount of fuel injected by an injector is more thandesired, the injector is calibrated such that less fuel is injected perinjection (e.g., the injection is compensated by a correctioncoefficient) in order to compensate for the injector degradation andmaintain the efficiency of the system.

Continuing to FIG. 5, a pump diagnostic routine 500 is shown.Specifically, routine 500 suspends injection in one of the fuel railswhile pumping in the fuel rail is resumed (or continues). In thismanner, pressure increase in the fuel rail can be correlated to theoperation of the pump and pump degradation can be indicated. In thisembodiment, the pump diagnostic routine is carried out after theinjector diagnostic routine when the pressure in the fuel has decreaseda known amount. However, in other embodiments, the pump diagnosticroutine may be carried out before the injector diagnostic routine orindependent of the injector diagnostic routine.

At 510 of routine 500, injection of fuel A is resumed in the singlecylinder. Next, at 512, injection of fuel B is suspended in the singlecylinder. As such, all cylinders receive only fuel A during the pumpdiagnostic routine.

Once injection of fuel B is suspended, pumping of fuel B into fuel railB is resumed at 514 of routine 500. Next, at 516, pressure increase infuel rail B is correlated to fuel pump degradation and then pumpdegradation is indicated at 518 of routine 500. For example, if thepressure increase in the fuel rail deviates from a predetermined orexpected value, degradation is indicated. As an example, if pressureincrease is less than expected, a fuel filter coupled to the fuel pumpmay be clogged or the pump may be leaking.

After fuel pump degradation is correlated to the pressure increase inthe fuel rail, routine 500 continues to 520 where operation of fuel pumpB is adjusted based on the correlation. For example, a calibrationcoefficient may be calculated and if the pump is pumping less fuel thandesired into the fuel rail per pump stroke, pump operation may beadjusted by the calibration coefficient such that more fuel is pumpedinto the fuel rail per pump stroke. Further, a diagnostic code may besent to the engine controller indicating degradation of the pump and theneed for service, for example.

FIGS. 6A and 6B show an example of fuel injection timing 600 andcorresponding fuel pressure change 610 in a fuel rail during an injectordiagnostic routine in a four cylinder engine. In the example of FIGS. 6Aand 6B only one injector is tested during the injector diagnosticroutine. Prior to an injector diagnostic routine, the fuel pressure inthe fuel rail is maintained at a normal operating pressure and normalpump strokes are issued. In some embodiments, as shown at 610, at thestart of the injector diagnostic routine, fuel pressure in the fuel railis increased (e.g., via more or larger pump strokes) before pumping issuspended. As shown, for each injection, the pressure in the fuel raildrops.

FIGS. 7A and 7B show another example of fuel injection timing 700 andcorresponding fuel pressure change 710 during an injector diagnosticroutine. In the example of FIGS. 7A and 7B, multiple injectors aretested during the injector diagnostic routine in a four cylinder engine.In the sequence shown at 700, all four injector are fired at differenttimes and the corresponding fuel pressure profile 710 may be used tocalculate a correction coefficient for each injector.

Thus, during engine operating conditions in which both fuels are notdesired for operation (e.g., one or both fuels may be used), pumping maybe suspended in one of the fuel rails allowing its injectors to beisolated for testing. Further, operation of the corresponding fuel pumpmay be subsequently assessed. As such, diagnostic routines for the fuelinjectors and fuel pumps may be carried out without significantlyinterfering with engine operation.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A multi-fuel injection method for an engine including first andsecond rails and first and second pumps, comprising: when multi-fueloperation is not needed: suspending pumping of a second fuel into thesecond rail while injecting a first fuel to all but a single enginecylinder; and while pumping is suspended in the second rail, injectingthe second fuel into the single engine cylinder and correlating pressuredecrease in the second rail to injector degradation.
 2. The method ofclaim 1, wherein injector degradation is indicated when the pressuredecrease is less than a predetermined value.
 3. The method of claim 1,wherein injector degradation is indicated when the pressure decrease isgreater than a predetermined value.
 4. The method of claim 1, furthercomprising: resuming injection of the first fuel to the single enginecylinder and suspending injection of the second fuel; and whileinjection of the second fuel is suspended, resuming pumping of thesecond fuel to the second rail and correlating pressure increase in thesecond rail to operation of the second pump.
 5. The method of claim 4,wherein degradation of the second pump is indicated when the pressureincrease deviates from a predetermined value.
 6. The method of claim 1,wherein each fuel injector of each cylinder of a plurality of enginecylinders is sequentially isolated to generate respective correlationsfor each injector.
 7. The method of claim 1, wherein the second fuel isinjected to the single engine cylinder through a predetermined number ofinjections.
 8. A method for controlling fuel injection of a dual fuelengine which includes first and second fuel rails and first and secondfuel pumps, comprising: when both fuels are not needed: suspendingpumping of a second fuel into the second fuel rail while injecting afirst fuel to all but a first group of cylinders of the engine; whilepumping is suspended in the second fuel rail, injecting the second fuelinto the first group of cylinders, and correlating pressure decrease inthe second fuel rail to injector degradation; and adjusting fuelinjection of the second fuel in the first group of cylinders based onthe correlation once pumping of the second fuel is resumed by the secondpump.
 9. The method of claim 8, wherein injector degradation isindicated when the pressure decrease deviates from a predeterminedvalue, and wherein the first group of cylinders is a single cylinder.10. The method of claim 8, further comprising: resuming injection of thefirst fuel to the first group of cylinders and suspending injection ofthe second fuel; while injection of the second fuel is suspended,resuming pumping of the second fuel to the second fuel rail andcorrelating pressure increase in the second fuel rail to operation ofthe second fuel pump; and adjusting operation of the second fuel pumpbased on the correlation of pressure increase and pump operation. 11.The method of claim 10, wherein pump degradation is indicated when thepressure deviates from a predetermined value.
 12. The method of claim 8,wherein the first fuel is gasoline and the second fuel is ethanol.
 13. Asystem for an engine in a vehicle, comprising: a plurality of cylinders,each cylinder having a first and second injector for first and secondfuels, respectively, where the first injector is coupled to a first fuelrail and the second injector is coupled to a second fuel rail; and acontrol system comprising a computer readable storage medium, the mediumcomprising instructions for: during a first condition, injecting fuel toall cylinders via the first injectors; and during a second conditionwhen the first and second fuels are not needed: injecting fuel to allbut one cylinder via the first injectors, and injecting fuel to the onecylinder via only the second injectors; and suspending pumping of fuelinto the second fuel rail while continuing pumping of fuel into thefirst fuel rail.
 14. The system of claim 13, wherein the first injectorsinject a first fuel and the second injectors inject a second fuel. 15.The system of claim 14, wherein the first condition includes operatingconditions in which only one fuel is used and a diagnostic routine isnot being carried out.
 16. The system of claim 14, wherein the secondcondition includes operating conditions in which both fuels are used anda diagnostic routine is being carried out.
 17. The system of claim 14,further comprising instructions for, during a third condition, injectingall cylinders via the first and second injectors where both the firstand second fuels are needed.
 18. The system of claim 17, wherein thethird condition includes operating conditions in which both fuels areused.
 19. The system of claim 13, further comprising, during the secondcondition and while pumping is suspended in the second fuel rail,correlating pressure decrease in the second fuel rail to injectoroperation.
 20. The system of claim 19, wherein injector degradation isindicated when the pressure decrease deviates from a predeterminedvalue.